I gather that you must never run them totally empty, so let's say you aim for 5 psi when the camper is off, how many weeks/months would it take for that pressure to totally go, I'm guessing that it's going to lose it just like a vehicles tyre will.

I'm thinking of during the Winter months or any time when the camper isn't going to carried for a while, it could become an issue if you forget to keep an eye on the pressure.

Easily fixed,as you've installed compressor under bonnet, its output going backwards under car to axleadd a 'T' piece and off that a cheap gauge through any available slot/hole in cabin floor, then Gauge somewhere in sight

Cold weather seemed to create loss in my system over Winter with my push fittings but better screw types reportedly don't lose much at all

I don't fancy that idea for a few reasons, not keen on drilling holes in the cab, haven't found a suitable place in the cab to put a gauge and if I did, I don't like the idea of it being pressurised constantly, I prefer to cut the pressure off at a valve so I might as well pop the bonnet to look at that gauge basically.

I didn't like the idea of push fit hoses from the start, I went straight for the screw in type.

Better fittings are a good idea, mine came with these, my own leaks may have been down to a faulty valve (now changed out) so I'll know after Winter about that, certainly its been spot on since over summer anyway,

usually on a cab there will be either a rubber bung as a drain somewhere beneath a mat out of sight you can make a slit in big enough to pass pipe through, or there's alway the large wiring loom rubber grommets in bulkhead behind dash you can squeeze it through if needed,

pressure is pretty minimal I've never seen a gauge fail yet even the cheap ones, as far as size goes I agree for what we need either one off a divers scuba rig, or an old fire extinguisher though not marked in PSI you could easily ascertain where needle needs to be for 60PSI or similar.

for what you need you can just pop the bonnet once a week, and beyond serious off-road I don't believe running them empty for a few days does that much damage frankly, I know I did in the past without apparent damage

I know that there's a warning in the instructions about running these bags empty, damage will occur.I did wonder about that, since you mentioned serious off roading I'm guessing that it's full extension rather than compression of the bag that's likely to do the damage.

My only other thought is if you have to jack the vehicle up via a chassis rail rather than the axle, is it best to inflate the bags some more before hand?